diff --git a/exceptiongroup/__init__.py b/exceptiongroup/__init__.py
index ef2a381..d560757 100644
--- a/exceptiongroup/__init__.py
+++ b/exceptiongroup/__init__.py
@@ -33,6 +33,7 @@ def __init__(self, message, exceptions, sources):
                 raise TypeError(
                     "Expected an exception object, not {!r}".format(exc)
                 )
+        self.message = message
         self.sources = list(sources)
         if len(self.sources) != len(self.exceptions):
             raise ValueError(
@@ -41,6 +42,16 @@ def __init__(self, message, exceptions, sources):
                 )
             )
 
+    # copy.copy doesn't work for ExceptionGroup, because BaseException have
+    # rewrite __reduce_ex__ method.  We need to add __copy__ method to
+    # make it can be copied.
+    def __copy__(self):
+        new_group = self.__class__(self.message, self.exceptions, self.sources)
+        new_group.__traceback__ = self.__traceback__
+        new_group.__context__ = self.__context__
+        new_group.__cause__ = self.__cause__
+        return new_group
+
 
 from . import _monkeypatch
 from ._tools import split, catch
diff --git a/exceptiongroup/_tests/test_exceptiongroup.py b/exceptiongroup/_tests/test_exceptiongroup.py
deleted file mode 100644
index e67928c..0000000
--- a/exceptiongroup/_tests/test_exceptiongroup.py
+++ /dev/null
@@ -1,2 +0,0 @@
-import traceback
-from exceptiongroup import ExceptionGroup, split, catch
diff --git a/exceptiongroup/_tests/test_tools.py b/exceptiongroup/_tests/test_tools.py
new file mode 100644
index 0000000..b385bc6
--- /dev/null
+++ b/exceptiongroup/_tests/test_tools.py
@@ -0,0 +1,117 @@
+from exceptiongroup import ExceptionGroup, split
+
+
+def raise_error(err):
+    raise err
+
+
+def raise_error_from_another(out_err, another_err):
+    # use try..except approache so out_error have meaningful
+    # __context__, __cause__ attribute.
+    try:
+        raise another_err
+    except Exception as e:
+        raise out_err from e
+
+
+def test_split_for_none_exception():
+    matched, unmatched = split(RuntimeError, None)
+    assert matched is None
+    assert unmatched is None
+
+
+def test_split_when_all_exception_matched():
+    group = ExceptionGroup(
+        "Many Errors",
+        [RuntimeError("Runtime Error1"), RuntimeError("Runtime Error2")],
+        ["Runtime Error1", "Runtime Error2"]
+    )
+    matched, unmatched = split(RuntimeError, group)
+    assert matched is group
+    assert unmatched is None
+
+
+def test_split_when_all_exception_unmatched():
+    group = ExceptionGroup(
+        "Many Errors",
+        [RuntimeError("Runtime Error1"), RuntimeError("Runtime Error2")],
+        ["Runtime Error1", "Runtime Error2"]
+    )
+    matched, unmatched = split(ValueError, group)
+    assert matched is None
+    assert unmatched is group
+
+
+def test_split_when_contains_matched_and_unmatched():
+    error1 = RuntimeError("Runtime Error1")
+    error2 = ValueError("Value Error2")
+    group = ExceptionGroup(
+        "Many Errors",
+        [error1, error2],
+        ['Runtime Error1', 'Value Error2']
+    )
+    matched, unmatched = split(RuntimeError, group)
+    assert isinstance(matched, ExceptionGroup)
+    assert isinstance(unmatched, ExceptionGroup)
+    assert matched.exceptions == [error1]
+    assert matched.message == "Many Errors"
+    assert matched.sources == ['Runtime Error1']
+    assert unmatched.exceptions == [error2]
+    assert unmatched.message == "Many Errors"
+    assert unmatched.sources == ['Value Error2']
+
+
+def test_split_with_predicate():
+    def _match(err):
+        return str(err) != 'skip'
+
+    error1 = RuntimeError("skip")
+    error2 = RuntimeError("Runtime Error")
+    group = ExceptionGroup(
+        "Many Errors",
+        [error1, error2],
+        ['skip', 'Runtime Error']
+    )
+    matched, unmatched = split(RuntimeError, group, match=_match)
+    assert matched.exceptions == [error2]
+    assert unmatched.exceptions == [error1]
+
+
+def test_split_with_single_exception():
+    err = RuntimeError("Error")
+    matched, unmatched = split(RuntimeError, err)
+    assert matched is err
+    assert unmatched is None
+
+    matched, unmatched = split(ValueError, err)
+    assert matched is None
+    assert unmatched is err
+
+
+def test_split_and_check_attributes_same():
+    try:
+        raise_error(RuntimeError("RuntimeError"))
+    except Exception as e:
+        run_error = e
+
+    try:
+        raise_error(ValueError("ValueError"))
+    except Exception as e:
+        val_error = e
+
+    group = ExceptionGroup(
+        "ErrorGroup", [run_error, val_error], ["RuntimeError", "ValueError"]
+    )
+    # go and check __traceback__, __cause__ attributes
+    try:
+        raise_error_from_another(group, RuntimeError("Cause"))
+    except BaseException as e:
+        new_group = e
+
+    matched, unmatched = split(RuntimeError, group)
+    assert matched.__traceback__ is new_group.__traceback__
+    assert matched.__cause__ is new_group.__cause__
+    assert matched.__context__ is new_group.__context__
+    assert unmatched.__traceback__ is new_group.__traceback__
+    assert unmatched.__cause__ is new_group.__cause__
+    assert unmatched.__context__ is new_group.__context__
diff --git a/exceptiongroup/_tools.py b/exceptiongroup/_tools.py
index 5ab124c..3922c81 100644
--- a/exceptiongroup/_tools.py
+++ b/exceptiongroup/_tools.py
@@ -2,9 +2,22 @@
 # Core primitives for working with ExceptionGroups
 ################################################################
 
+import copy
 from . import ExceptionGroup
 
+
 def split(exc_type, exc, *, match=None):
+    """ splits the exception into one half (matched) representing all the parts of
+    the exception that match the predicate, and another half (not matched)
+    representing all the parts that don't match.
+
+    Args:
+        exc_type (type of exception): The exception type we use to split.
+        exc (BaseException): Exception object we want to split.
+        match (None or func): predicate function to restict the split process,
+            if the argument is not None, only exceptions with match(exception)
+            will go into matched part.
+    """
     if exc is None:
         return None, None
     elif isinstance(exc, ExceptionGroup):
@@ -13,9 +26,9 @@ def split(exc_type, exc, *, match=None):
         rests = []
         rest_notes = []
         for subexc, note in zip(exc.exceptions, exc.sources):
-            match, rest = ExceptionGroup.split(exc_type, subexc, match=match)
-            if match is not None:
-                matches.append(match)
+            matched, rest = split(exc_type, subexc, match=match)
+            if matched is not None:
+                matches.append(matched)
                 match_notes.append(note)
             if rest is not None:
                 rests.append(rest)
@@ -128,5 +141,18 @@ def __exit__(self, etype, exc, tb):
             exceptiongroup_catch_exc.__context__ = saved_context
 
 
-def catch(cls, exc_type, handler, match=None):
+def catch(exc_type, handler, match=None):
+    """Return a context manager that catches and re-throws exception.
+        after running :meth:`handle` on them.
+
+    Args:
+        exc_type: An exception type or A tuple of exception type that need
+            to be handled by ``handler``.  Exceptions which doesn't belong to
+            exc_type or doesn't match the predicate will not be handled by
+            ``handler``.
+        handler: the handler to handle exception which match exc_type and
+            predicate.
+        match: when the match is not None, ``handler`` will only handle when
+            match(exc) is True
+    """
     return Catcher(exc_type, handler, match)